In October 2014，Nara Medical University Library introduced a new library system of a "self-checkout machine", allowing users to borrow and return books and journals without requiring the assistance of library staff. This study examined the usefulness of this machine to library users after their introduction. To measure user onvenience, data was collected from the library system log for the period between April and September in 2014 and 2015 (before and after the introduction). The research was done using the following method. Tne first step was to examine the change in the number of library materials borrowed during the targeted periods in 2014 and 2015. The second step was to compare the number of items borrowed during opening hours when library staff were present and during opening hours when library staff were not present. Next, the number of items borrowed per user group was calculated. And the third step was to examine the trends in the use of the self-checkout machine. Compared to the targeted period in 2014, the number of borrowed items increased by 39.8% during the targeted period in 2015. The number of items borrowed per user group also increased after the introduction of the self-checkout machine. The results showed that library users frequently used the self-checkout machine during opening hours when library staff were not present. The self-checkout machine was thought to help library users study and to contribute to the improvement of our library services.